diff --git a/app-android/app/src/main/java/de/tutao/tutanota/AndroidMobileSystemFacade.kt b/app-android/app/src/main/java/de/tutao/tutanota/AndroidMobileSystemFacade.kt
index a6b96f66e039..822165ca6f6a 100644
--- a/app-android/app/src/main/java/de/tutao/tutanota/AndroidMobileSystemFacade.kt
+++ b/app-android/app/src/main/java/de/tutao/tutanota/AndroidMobileSystemFacade.kt
@@ -4,9 +4,9 @@ import android.Manifest
 import android.content.ActivityNotFoundException
 import android.content.ClipData
 import android.content.Intent
-import android.content.Intent.EXTRA_REFERRER
 import android.net.Uri
 import android.provider.Settings
+import android.util.Base64
 import android.util.Log
 import androidx.biometric.BiometricManager
 import androidx.biometric.BiometricPrompt
@@ -15,6 +15,7 @@ import androidx.core.content.ContextCompat.startActivity
 import androidx.core.content.FileProvider
 import androidx.fragment.app.FragmentActivity
 import de.tutao.tutashared.CredentialAuthenticationException
+import de.tutao.tutashared.SystemUtils
 import de.tutao.tutashared.atLeastTiramisu
 import de.tutao.tutashared.credentials.AuthenticationPrompt
 import de.tutao.tutashared.data.AppDatabase
@@ -23,7 +24,7 @@ import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
 import java.io.File
 import java.io.IOException
-import de.tutao.tutashared.SystemUtils
+import java.nio.charset.Charset
 
 
 class AndroidMobileSystemFacade(
@@ -37,6 +38,8 @@ class AndroidMobileSystemFacade(
 	companion object {
 		private const val TAG = "SystemFacade"
 		const val APP_LOCK_METHOD = "AppLockMethod"
+		const val TUTA_INTENT_ACTION = "TUTA_INTEROP"
+		const val TUTA_INTENT_INTEROP_DATA = "TUTA_INTEROP_DATA"
 	}
 
 	override suspend fun openLink(uri: String): Boolean {
@@ -188,11 +191,13 @@ class AndroidMobileSystemFacade(
 
 	override suspend fun openCalendarApp(query: String) {
 		val decodedQuery = Base64.decode(query.toByteArray(), Base64.DEFAULT).toString(Charset.defaultCharset())
+		val targetPackageId = activity.getString(R.string.package_name).replace("calendar", "tutanota")
 
 		val intent = Intent()
+		intent.setPackage(targetPackageId)
 		intent.setAction(Intent.ACTION_EDIT)
-		intent.putExtra(EXTRA_REFERRER, BuildConfig.APPLICATION_ID)
-		intent.setData(Uri.parse("tutacalendar://interop?${decodedQuery}"))
+		intent.putExtra(TUTA_INTENT_ACTION, "interop")
+		intent.setData(Uri.parse("tutacalendar://interop?$decodedQuery"))
 
 		try {
 			startActivityForResult(activity, intent, 0, null)
diff --git a/app-android/app/src/main/java/de/tutao/tutanota/MainActivity.kt b/app-android/app/src/main/java/de/tutao/tutanota/MainActivity.kt
index 7102dd48d7df..4ddc9ed4424f 100644
--- a/app-android/app/src/main/java/de/tutao/tutanota/MainActivity.kt
+++ b/app-android/app/src/main/java/de/tutao/tutanota/MainActivity.kt
@@ -8,7 +8,7 @@ import android.content.ClipData
 import android.content.ClipboardManager
 import android.content.ComponentName
 import android.content.Intent
-import android.content.Intent.EXTRA_REFERRER
+import android.content.Intent.ACTION_EDIT
 import android.content.pm.PackageManager
 import android.content.res.Configuration
 import android.graphics.Color
@@ -454,12 +454,14 @@ class MainActivity : FragmentActivity() {
 			return@launch
 		}
 
-		if (data != null && data.toString().startsWith("tutamail://") && data.host == "interop") {
-			val caller = intent.getStringExtra(EXTRA_REFERRER)
+		val isInteropCall = intent.action == ACTION_EDIT && intent.getStringExtra(TUTA_INTENT_ACTION) == "interop"
+		val isTrustedCaller = callingPackage == BuildConfig.APPLICATION_ID.replace(
+			"tutanota",
+			"calendar"
+		)
 
-			if (caller?.startsWith("de.tutao") == true) {
-				openContactEditor(data)
-			}
+		if (data != null && isInteropCall && isTrustedCaller) {
+			openContactEditor(data)
 		}
 
 		if (intent.action != null && !intent.getBooleanExtra(ALREADY_HANDLED_INTENT, false)) {
@@ -809,6 +811,8 @@ class MainActivity : FragmentActivity() {
 		const val OPEN_CONTACT_EDITOR_CONTACT_ID = "contactId"
 		const val OPEN_USER_MAILBOX_MAILID_KEY = "mailId"
 		const val ALREADY_HANDLED_INTENT = "alreadyHandledIntent"
+		const val TUTA_INTENT_ACTION = "TUTA_INTEROP"
+
 		private const val TAG = "MainActivity"
 		private var requestId = 0
 
diff --git a/app-android/calendar/src/main/java/de/tutao/calendar/AndroidMobileSystemFacade.kt b/app-android/calendar/src/main/java/de/tutao/calendar/AndroidMobileSystemFacade.kt
index d7401d4eb155..732d0f5b7590 100644
--- a/app-android/calendar/src/main/java/de/tutao/calendar/AndroidMobileSystemFacade.kt
+++ b/app-android/calendar/src/main/java/de/tutao/calendar/AndroidMobileSystemFacade.kt
@@ -4,7 +4,6 @@ import android.Manifest
 import android.content.ActivityNotFoundException
 import android.content.ClipData
 import android.content.Intent
-import android.content.Intent.EXTRA_REFERRER
 import android.net.Uri
 import android.provider.Settings
 import android.util.Base64
@@ -34,12 +33,13 @@ class AndroidMobileSystemFacade(
 	private val activity: MainActivity,
 	private val db: AppDatabase,
 ) : MobileSystemFacade {
-
 	private val authenticationPrompt = AuthenticationPrompt()
 
 	companion object {
 		private const val TAG = "SystemFacade"
 		const val APP_LOCK_METHOD = "AppLockMethod"
+		const val TUTA_INTENT_ACTION = "TUTA_INTEROP"
+		const val TUTA_INTENT_INTEROP_DATA = "TUTA_INTEROP_DATA"
 	}
 
 	override suspend fun openLink(uri: String): Boolean {
@@ -187,11 +187,13 @@ class AndroidMobileSystemFacade(
 
 	override suspend fun openMailApp(query: String) {
 		val decodedQuery = Base64.decode(query.toByteArray(), Base64.DEFAULT).toString(Charset.defaultCharset())
+		val targetPackageId = activity.getString(R.string.package_name).replace("calendar", "tutanota")
 
 		val intent = Intent()
+		intent.setPackage(targetPackageId)
 		intent.setAction(Intent.ACTION_EDIT)
-		intent.putExtra(EXTRA_REFERRER, BuildConfig.APPLICATION_ID)
-		intent.setData(Uri.parse("tutamail://interop?${decodedQuery}"))
+		intent.putExtra(TUTA_INTENT_ACTION, "interop")
+		intent.setData(Uri.parse("tutamail://interop?$decodedQuery"))
 
 		try {
 			startActivityForResult(activity, intent, 0, null)